I saw quoted in the name of the Lubavitcher Rebbe that we learn from here that when a Jewish child is in danger, it’s not the time to be thinking about your own spiritual failings and working on your own teshuvah. Go out and save him! Had Reuvain not gone off to do his own teshuvah, who knows if he might not have been able to save Yosef.
The Beis Yisrael takes the opposite view. When a person does teshuvah it elevates not only the individual, but it elevates those around him/her, and even has an effect on the whole world. Reuvain’s teshuvah was not a distraction from his effort to save Yosef – it was a means to that same end. Had his teshuvah been complete, the brothers would have given up their plan and he would have been able to bring Yosef home.
At the risk of extrapolating too much from a single issue, it seems that this is not just a machlokes about how to read an isolated Rashi, but is representative of two different world views. If I recall correctly, the Shem m’Shmuel somewhere quotes a mashal from the Kotzker: a prison warden dropped another poor soul into the dark prison pit which was holding two other prisoners. One of the two reached out and tried to help the new man cope. Day after day he tried to show the new man how to eat so he doesn’t spill his food in the pitch black darkness of the dungeon, how to use his spoon to sip the soup, etc. but it was hard going, and what was especially frustrating was that his fellow prisoner offered no help at all. “Won’t you do anything to help this poor fellow?” he finally screamed in frustration. “I am helping him,” his fellow dungeon-mate answered. “The whole time you have been using your spoon to try to show him how to eat in the dark I’ve been using my spoon to dig a hole in the wall and let in some light.”
2. A very nice vort from the Chiddushei haRI"M: When Yosef chances upon the man, or the malach, who points him in the direction of his brothers, the Torah tells us (37:15), “VaYisha’leihu ha’ish leimor ‘Mah tivakesh?’” Was the man asking him a question (vayisha’leihu) or was the man telling him something (leimor)? The Ch. haRI”M explains that the malach knew that Yosef was about to descend into the galus of Egypt and his brothers and father would eventually follow. The malach was telling Yosef that the key to survival in that galus is to keep asking yourself the question, “Mah tevakeh?” -- What am I really looking for in life?
The Beis Yisrael suggests that the malach may have been hinting that it’s “mah” -- Mah Hashem Elokecha sho’el… ki im l’yirah… -- that you always need to be searcing for.